The present invention relates to a method for recovering and treating the brine from water softener regeneration, and more particularly, to a closed system for regenerating cation exchange water softeners with potassium chloride or sodium chloride and, then, softening the regenerant wastes (brine) produced during the regeneration.
Traditionally, cation exchange water softeners are regenerated with a sodium chloride (NaCl) regenerating material. An excess of NaCl is used. The sodium ions replace the magnesium and calcium ions trapped on the ion exchange resin. Calcium chloride and magnesium chloride are produced. Those chlorides, along with the excess NaCl, are dumped into the sewers and eventually find their way into the nation's rivers, streams and lakes.
This creates an ecologically undesirable result. Since all of these materials in the regenerant wastes are soluble, their discharge into a water course adds significantly to the total dissolved solids which must be handled by a downstream user of the water course when he attempts to treat the water to make it suitable for domestic or industrial consumption. For this reason, pollution control laws already enacted or about to be enacted may in the future prohibit discharge of high concentration soluble inorganic salts into waters. Accordingly, it becomes necessary to attempt to prevent such a discharge or regenerant brine from cation exchange water softeners.
For this reason, Popper in U.S. Pat. No. 3,528,912 discloses a process for treating regenerate brine with sodium carbonate to precipitate calcium and magnesium carbonate. Regenerate liquor is flowed through an ion-exchange column in an upflow mode, captured, and treated with the sodium carbonate prior to being filtered. The filtrate is replenished with sodium ions and recycled back to the ion-exchange column to effect further regeneration. At Col. 3, lines 52-67, it is explained that problems may occur with the precipitate if it becomes gelatinous. Popper handles these problems by use of a special filtering technique.
Odland U.S. Pat. No. 3,977,968, however, indicates that a more desirable solution is to dilute the regenerate brine so that the alkaline earth metal content is less than 16,000 ppm, calculated as calcium carbonate. Odland states that only in this way it is truly possible to avoid formation of a gelatinous precipitate and make the process workable.
Still, by diluting the regenerate brine in this manner, difficulties are encountered in producing a workable closed system. That is, in a closed system, it is imparative from a processing and equipment standpoint that the treatment chemicals be as concentrated as possible. This means that the volume of sludge generated must be equal to or greater than the displacement volume of the chemicals added for brine treatment. Should the volume of the treatment chemicals be greater than the volume lost from the sludge, cyclic operation will give an even increasing dilution or volume of regenerate, which ultimately causes failure of the system. In turn, dilution of the regenerant brine merely aggrevates the problem.
Accordingly, the need exists for an effective and efficient means for recovering and treating the brine from the regeneration cycle of cation exchange water softeners. More importantly, a need exists for a workable closed system for regenerating cation exchange water softeners, and then, recovering and treating the brine in an ecologically beneficial manner.